Altitude compensated carburetor



United States Patent Ce 3,011,770 Patented Dec. 5, 1961 The present invention relates to a temperature and altitude compensated carburetor and more particularly one in which the quantity of air ow is adapted to be varied with changes in altitude or temperature to maintain a substantially constant air-fuel ratio.

While it has long been known that changes in tempera- Y ture and yaltitude vary the fuel-air ratio, e.g., increase the ratio with increases in either temperature or altitude, it has been 'the practice to compensate for thisetfect --by modifying the quantity of fuel supplied. In the present invention, however, a vunique device has been developed in which fuel ow remains constant for a given induction passage mass air ow while the quantity of air tlowing to the engine is modied in accordance with variations in ambient temperature or pressure.

It is, of course, desirable to maintain a substantially constant fuel-air ratio under all normal operating conditions in order for the engine to'function properly bo-th from a point of view of power and economy. In the present device an air bypass is provided, the ow through which is controlled by 1a diaphragm type valve which is moved to open or close the bypass in accordance with variations in ambient operathig conditions. The source of power for moving -the subject air bypass valve is a vacuum force created by induction passage air ow. The value of vacuum force operative on the diaphragm valve is, however, uniquely controlled by a bellows bleed valve member such that the position of the bypass valve is determined by the position of the bellows valve although the latter valve need do no work in actually moving such valve.

The use of the unique bellows type bleed control valve makes the subject device extremely sensitive to changes in ambient operating conditions and hence renders the present device considerably more accurate in controlling the fuel-air ratios than has been achievedwith previous devices.

The details as well as other objects and advantages of the present invention will be apparent from a perusal of the detailed description which follows.

The drawing is a schematic representation of a carburetor embodying the subject invention.

A carburetor is shown generally at 10 and includes cover, oat bowl, and throttle casings 12 14 and 16 through which an air induction passage 18 is formed. A conventional main venturi 20 is formed in oat bowl casing 14 Iand includes a booster or fuel supply venturi 22 disposed therein. A choke valve 24 is mounted in the cover casing 12 and is adapted to control the fuel-#air ratio to provide an enrichment thereof during engine starting conditions. A throttle valve 26 is rotatably disposed in throttle body casing 16 to control the quantity of air ow through induction passage 18.

A fuel reservoir 28 is formed in float bowl casing 14 and is `adapted to supply fuel to a main fuel nozzle 29 which connects with booster venturi 22. 'in order to f2 provide an enrichment of the fuelair ratio during high power demand conditions, a conventional power piston device 3i) is provided. During light load operating conditions, manifold vacuum in conduit 32 is of suciently high value to retain the power piston 34 in its upper position as shown in the drawing, and to thereby comv press spring 36. Rod 38 secured to power piston 34 includes an enlarged end or valve member 39 which blocks fuel ow through an orifice 40 when piston 34 is in its upper position. Under these circumstances fuel will be drawn from fuel reservoir 28 through continuously open oriiice 42 to a passage 44 which supplies fuel nozzle 29. In'the event of a high powerdemand situation, increased engine load' will cause manifold vacuum in conduit 32 to drop permitting spring 36 'to move metering rod 38 downwardly opening valve 39 supplying additional fuel to passage 44 through oriiice 40. The operation of the power piston will be considered further in regard to the air bypass mechanism which will now be described.

An air bypass isprovided around main Venturi 20 and includes passages :and chambers 46, 48 and 50. These passages are formed in an extension of the float bowl casing or if desired may be formed in a separate casing which may be suitably fixed to the float bowl casing. The air flow through the air bypass passages is controlled by a diaphragm valve 52 which is adapted to be normally seated `against an annular seat 54 by a spring member 56. One end of spring 56 `seats against a cover casing 5S and the other end of which biases against a diaphragm reinforcing washer 60. Diaphragm 52 is peripherally clamped lbetween casing 14 and cover casing 58.

A sleeve valve member 62 is slidably mounted within a cylindrical opening formed in casing 14. Sleeve valve member 62 is secured at one end to diaphragm valve member 52. A longitudinal passage 64 is formed through sleeve valve member 62 and communicates with a chamber 66 formed by diaphragm 52 and cover casing 58. The other end of passage 64 is open to the ambient pressure extent in air bypass chamber 48. An annularly relieved portion 68 is formed in sleeve valve 62 and communicates at its inner end with longitudinal passage 64 through a port 70. Relieved sleeve valve portion 6-8 valso communicates with a conduit 72 formed in casing 14 and the other end of which conduit openly communicates with the throat of main venturi 20. Thus a vacuum force exists in conduit 72 and the value of which varies with the mass of air ow through the venturi. Under low air flow conditions the vacuum in conduit 72 is supplemented with manifold vacuum through a Xed bleed passage 74 communicating with manifold vacuum conduit 76.

Inasmuch as the upper end of slide valve passage 64 isv open to generally atmospheric pressure, the vacuum force in chamber 66 will be normally insufcient to overcome the force of spring 56. An ambient pressure and temperature responsive bellows '78 is mounted from a cover casing through a threaded stud member 82 and in# cludes a at valve member 84 fixed thereto and normally disposed proximate the open upper end of sleeve valve passage 64. It is apparent, therefore, that bellows valve member 84 coacts with the upper end of sleeve valve passage 64 to provide a variable atmospheric bleed which determines the vacuum force within chamber 66. In other Words, as bellows valve member 84 approaches the upper end of passage 64 the atmospheric bleed is reduced and the vacuum in chamber 66 increased thereby permitting diaphragm valve 52 to be opened and bypass air around main venturi 20. A reduction in the amount of atmospheric bleed through sleeve valve passage V64 and hence the position of diaphragm bypass valve 52 is therefore determined by -the ambient operating conditions. To illustrate, as the carburetor would be operated in a more raried atmosphere, as in mountainous areas, bellows '78 would expand due to the decreased' ambient pressure and in so doing would reduce the atmospheric bleed into passage 64 and correspondinglyrpermit the vacuum in chamber 66 to open the diaphragm bypass valve to maintain a constant fuel-air ratio.

At increasing altitudes there is less manifold vacuum available to hold power piston 34 in its upper or economy position and inasmuch as spring 36, against which manifold vacuum operates, does not sense altitude the power valve 39 would open at relatively low values of air flow where power is not required. Such operation would, of course, be detrimental to engine economy. To prevent this occurrence, lpower piston vacuum is decreased slightly at sea level as will now be considered. First, it is to be noted that manifold vacuum is supplied by conduit 76 which terminates at one end posteriorly of throttle valve 26 and which communicates near its other end through an oriice 86 with conduit 32. A second annu- `larly relieved portion 88 is lformed on sleeve valve 62. With the diaphragm air bypass valve closed relieved portion y83 `of the valve member bleeds atmospheric air through a casing passage 90 and orifice 92 into vacuum conduit 32. Thus while a relatively greater vacuum force is available to act on power piston34 this vacuum force is bled-down through oriiice V92 during this sea level condition. As ambient air pressure decreases with increased altitude, however, sleeve valve member 62 is moved downwardly with diaphragm valve 52 and in so doing moves recessed portion 88 out of registry with atmospheric bleed port 92 thereby relatively increasing the force of vacuum acting on power piston 34 to retain the latter in its upper or economy position.

vlt is also necessary with increases in altitude to increase the idle air flow to the engine since the low density air does not otherwise provide sufficient power to keep the engine idling properly. Idle air flow must be increased Without increasing fuel liow because the uncompensated fuel-air ratio is excessively rich. When bypass valve 52 is open, ambient pressure bleed 90 communicates through reduced portion 88 of valve member 62 with a port 94 in vacuum passage 76 thereby permitting an increased idle air llow around closed throttle 26. Y

It is thus apparent that a fully compensated carburetor is provided which will maintain a substantially constant fuel-air flow ratio under all normal operating conditions notwithstanding variations in ambient operating conditions.

l. A charge forming device for an internal combustion engine comprising an induction passage, a main venturi formed in said passage, a throttle valve rotatably disposed in said induction passage for controlling the quantity of air ow therethrough, a source of fuel, means for supplying fue] to said induction passage in accordance with the quantity of air flow therethrough, a power piston device for increasing the quantity of fuel ow during high power demand operating conditions, a conduit communieating said power piston device with said induction passage posteriorly of the throttle valve to maintain Vthe device in an inoperative condition during normal engine operation, passage means for bypassing air around said main venturi to maintain a constant fuel-air ratio under all ambient operating conditions, a valve device for controlling air dow through said air bypass passage means, said valve device including a servo operatively connected to a source of vacuum, a spring member normally biasing said valve device Ito block the dow of air through said air bypass passage, said servo vacuum force normally being of suflicient value to overcome said spring to open said valve device, a bleed passage intermediate said servo and said servo vacuum force, an ambient temperature and pressure device coacting with said atmospheric bleed passage to vary the vacuum force within said servo and to thereby control the degree of opening of said bypass valve device, and a second atmospheric bleed passage means controlled by said air bypass valve device for varying the vacuum force acting on said power piston device.

2. A charge forming device as set forth in claim l in which said air bypass valve device comprises a diaphragm, a spring element biasing said diaphragm to block air how through said air bypass passage means, a ported passage, a sleeve valve member slidably disposed within said ported passage and secured at one end to said diaphragm, a casing coacting with said diaphragm to define a chamber, a longitudinal passage formed through said sleeve valve member and communicating Vat one end with said chamber and at the other end open to ambient atmospheric pressure, a port in said sleeve valve member communicating Isaid servo vacuum force with said longitudinal passage, and further in which said ambient temperature and pressure responsive device includes a valve member adapted to coact with the end of said sleeve v'alverpassage open to ambient pressure whereby the vacuum forcekin said chamber may be varied. Y Y

3. A charge forming device for an internal combustion engine comprising an air induction passage, a main venturi formed in said induction passage, a throttle v alve rotatably disposed within said induction passage for con'- trolling the quantity of air flow therethrough, a source of fuel, means for supplying fuel lfrom said fuel source in accordance with the quantity of air ow through said induction passage, air passage means for bypassing air around `said main venturi, and a valve device associated with said bypass passage for controlling the quantity of air ilow therethrough in accordance with yambient operating conditions.

4. A charge forming device forY an internal combustion engine comprising an air induction passage, a main venturi formed in said induction passage, a throttle valve rotatably disposed within said induction passage for controlling the quantity of air flow therethrough, a source of fuel, means for supplying fuel from said fuel source in accordance with the quantity of air ow through said induction passage, a manifold vacuum responsive means for increasing fuel ow during high engine load operating conditions, air passage means for bypassing air'around said main venturi, and a valve device associated with said bypass passage for controlling the quantity of air flow therethrough in accordance with ambient operating conditions, said valve device coacting with the fuel dow increasing means to render the latter insensitive to air density variations.

5. A charge forming device for an internal combustion engine comprising 'an air induction passage, a main venturi vformed in said induction passage, a throttle valve rotatably disposed within said induction passage forl controlling the quantity of air iiow therethrough, iirst passage means adapted to bypass air around Ithe throttle when the latter is closed, a source of fuel, means for supplying Vfuel from said fuel source in accordance with the quantity of air ow through said induction passage, second air pas sage means for bypassing air around said main venturi, and a valve device associated with ysaid rst and second bypass passage means for controlling the quantity of air ow therethrough in accordance with ambient operating conditions.

6. A charge forming device for an internal combustion engine comprising an air induction passage, a main venturi formed in said induction passage, a throttle valve rortatably disposed within said induction passage for controlling the quantity of air flow therethrough, rst passage means adapted to bypass air around the throttle when the 3,0 1 1,770 5 6 latter is closed, a source of fuel, means for supplying fuel fuel flow increasing means to render the latter substantifrom said fuel source in accordance with the quantity of ally insensitive to air density variations. air flow through said induction passage, 'a manifold vacuum responsive means for increasing the fuel oW References Cited in the file 0f this patent during high engine load operating conditions, second air 5 passage means for bypassing air around said main ven- UNITED STATES PATENTS turi, and a valve device associated with said rst and 2,619,334 Tissier Nm, 25J 1952 second bypass passage means for controlling the quantity 2,675,792 Brown et a1 APT` 20, 1954 of air flow therethrough in accordance with ambient Oper- 2,873,958 Del-mond Feb, 17, 1959 ating`conditions, said valve device coacting with said 10 

